Charge imbalances between battery cells of a battery pack may result from manufacturing differences between battery cells or from the composition of materials from which the battery cells are fabricated. Charge imbalances between battery cells may be undesirable because some battery cells may have to be charged or discharged before other battery cells so that the full charge capacity of the battery may not be reached. However, timing of balancing charge between battery cells may also induce charge imbalance between battery cells. For example, if a first battery cell stack begins to drain or add charge to its battery cells while a second battery cell stack does not, charge imbalance between the battery cells of the two battery cell stacks may increase. Further, if the battery cell stacks are sourcing or sinking current during the charge balancing process, the cells being drained of charge via charge balancing circuitry may reach the upper or lower charging limit threshold before the remaining battery cells.
The inventors herein have recognized the above issues and developed an approach to address them. In particular, the inventors have developed a method for balancing charge of a battery pack, the battery pack comprising a plurality of battery cell stacks, comprising: balancing charge of at least one battery cell of the battery pack during a second battery cell charge balancing cycle responsive to at least one battery cell charge sample from a plurality of battery cells sampled during a first battery cell charge balancing cycle.
By applying battery cell charging information gathered during a first battery charge balancing cycle to a second battery charge balancing cycle, it may be possible to start balancing of battery cell stacks that have different numbers of battery cells electrically coupled in series at substantially the same time. Therefore, there may be less possibility of generating charge imbalance from the charge balancing process. For example, even though it may take different amounts of time to process battery cell charge balancing data for two battery cell stacks comprised of different numbers of battery cells, adjusting charge balance of the battery cells via the latest battery cell charge data can be delayed until charge balancing is started in a subsequent battery charge balancing cycle so that the time required to process the battery charge balancing data has substantially no affect on the start timing of battery cell charge balancing. In this way, charge balancing of a battery pack comprised of battery cell stacks having different numbers of battery cells may be improved.
The present description may provide several advantages. Specifically, the approach can reduce the possibility of inducing charge imbalance between battery cells via a battery charge balancing process. In addition, the approach may be accomplished with little or no cost as compared to prior approaches where battery charge imbalance may have been induced during the battery charge balancing process.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.